Ion implantation is an important process in semiconductor/microelectronic manufacturing. The ion implantation process is used in integrated circuit fabrication to introduce dopant impurities into semiconductor wafers. The desired dopant impurities are introduced into semiconductor wafers to form doped regions at a desired depth. The dopant impurities are selected to bond with the semiconductor wafer material to create electrical carriers and thereby alter the electrical conductivity of the semiconductor wafer material. The concentration of dopant impurities that are introduced determines the electrical conductivity of the doped region. Many impurity regions are necessarily created to form transistor structures, isolation structures and other electronic structures, which collectively function as a semiconductor device.
The dopant impurities are generally ions derived from a source dopant gas. An ion-source is used to ionize the dopant gas source into the various dopant ionic species. The ions produce a plasma environment within the ion chamber. The ions are subsequently extracted from the ion chamber in the form of a defined ion beam. The resultant ion beam is typically characterized by a beam current. Generally speaking, a higher beam current can allow more dopant ionic species to be available for implantation into a given workpiece, such as a wafer. In this manner, a higher implant dosage of the dopant ionic species can be achieved for a given flow rate of source dopant gas. The resultant ion beam may be transported through a mass analyzer/filter and then transported to the surface of a workpiece, such as a semiconductor wafer. The desired dopant ionic species of the beam penetrate the surface of the semiconductor wafer to form a doped region of a certain depth with desired electrical and/or physical properties.
Boron implantation has been widely used in the semiconductor industry to modify electrical properties of the doped regions and is recently gaining traction in other applications where desired regions are doped with impurities to tailor certain physical properties of the doped region. The increasing use for boron implant steps during device fabrication is requiring a need for an improved process for implantation of B ions that can offer improved B+ beam current (i.e., sustained or increased beam current generated without shortened ion source life). It should be understood that the terms “B ions”, “B active ions”, “B ionic species”, “B ionic dopant species” and “B+ ions” may be used interchangeably herein and throughout the specification. The ability to implant B ions at an improved B+ beam current will allow end-users to perform increasing boron implant steps with higher equipment throughput and gain productivity improvements.
Boron trifluoride (BF3) is a dopant gas source typically utilized in the semiconductor industry for boron implantation, and used as the benchmark for boron ion implantation performance. However, BF3 has proven limited in its ability to generate B+ ions and thereby establish the higher beam currently demanded by today's applications. In order to increase the generation of B+ ions, the end-user can change various process parameters. For example, the end-user can increase the energy inputted to the ion source, otherwise referred to in the industry as the operating arc voltage of the ion source. Alternatively, the extraction current can be increased. Still further, the flow rate of BF3 introduced into the ion source chamber can be increased. However, such changes in the operation of the ion implant chamber can result in detrimental impact on the ion source components and reduce the ion source lifetime as well as the efficiency of the ion source in generating a stable B+ ion beam during extended operation. A stable B+ ion beam is defined by the uniform beam profile and continuous supply of the B+ ion beam at a desired beam current without interruption that may be caused by beam glitching or drop in beam current output. For example, as the walls of the arc chamber increase in temperature during a typical ion implant process, active fluorine that is released from BF3 can more rapidly etch and erode the tungsten (W) chamber walls, which can cause the cathode (i.e., the source filament of an ion source chamber) to be more susceptible to increased deposition of W-containing deposits. The W-containing deposits reduce the ion source's ability to generate the threshold number of electrons necessary to sustain the plasma and generate B+ ions required to produce the necessary beam current. Additionally, more active fluorine ions are available to propagate the so-called detrimental “halogen cycle” by which increased chemical erosion of the ion source chamber wall and other chamber components can occur. Accordingly, operating the ion source chamber at higher energy levels in an attempt to increase ionization of BF3 to produce the necessary beam current has the potential for shorter ion-source life, thereby rendering this mode of operation undesirable. Additionally, higher flow rates of BF3 tends to produce more active fluorine ions that causes chemical erosion of the ion source chamber wall and undesirable deposition on high voltage components resulting in arcing. These process modifications tend to shorter ion-source life, thereby making such modes of operation undesirable.
Currently, there are no viable techniques for maintaining or increasing the beam current of B+ ion without damaging the ion source chamber components. As such, there remains an unmet need to develop compositions, systems and methods of use thereof to improve the beam current of the desired boron ion species without compromising the ion source life.